1. Field of the Invention
The present invention relates to mixer, or signal multiplier, circuits, and in particular, to such circuits which employ differential amplifiers.
2. Description of the Related Art
Signal multiplier circuits, commonly referred to as mixers, are well known in the art and are used in many applications. One form of mixer, in particular, which is often used relies upon and takes advantage of the logarithmic voltage versus current characteristics of a differential amplifier circuit which causes the output signal to be a linear and amplified function of the input signals. By taking advantage of such characteristics, a linear multiplier circuit can be realized. A number of examples of such circuits can be found in U.S. Pat. No. 3,689,752, the disclosure of which is incorporated herein by reference as background information about the related art.
However, such mixer circuits in their conventional form have a number of disadvantages. One disadvantage is that, due to the necessary stacking, or totem-pole coupling, of the transistors, the available voltage range of the output signal is limited. Accordingly, to achieve higher voltage ranges, a higher power supply voltage becomes required. A second disadvantage is that many such circuits require a relatively large number of transistors, thereby increasing the sources of and potential for the introduction of noise into the output signal. Therefore, it would be desirable to have an improved signal multiplier circuit which addresses such disadvantages of conventional multiplier circuits.